Complex microelectronic devices such as semiconductor chips typically require numerous connections to other electronic components. For example, a complex device including a semiconductor chip may require hundreds of electrical connections between the chip and one or more external devices. These electrical connections may be made using several alternative methods, including wire bonding, tape automated bonding and flip-chip bonding. Each of these techniques presents various problems including difficulty in testing the chip after bonding, long lead lengths, large areas occupied by the chip on a microelectronic assembly, and fatigue of the connections due to changes in size of the chip and the substrate during thermal expansion and contraction.
In many microelectronic devices, it is desirable to provide an electrical connection between components that can accommodate relative movement between the components. For example, where a semiconductor chip is mounted to a circuit board, thermal expansion and contraction of the chip and circuit board can cause the contacts on the chip to move relative to contacts on the circuit board. This movement can occur during operation of the device or during manufacturing operations (e.g. when soldering the chip to the circuit board).
One structure that has been used to successfully address the above-mentioned problems is commonly referred to as a connection component such as that disclosed in certain preferred embodiments of commonly assigned U.S. Pat. Nos. 5,148,265, 5,148,266 and 5,455,390, the disclosures of which are hereby incorporated by reference herein. Connection components typically include a dielectric sheet having terminals thereon and flexible leads that are used to electrically interconnect the terminals with contacts on a microelectronic element, such as a semiconductor chip or wafer. The flexible leads permit thermal expansion and contraction of the microelectronic element and connection component, while maintaining a reliable electrical connection therebetween. The terminals of the connection component may be used to test the assembly, and/or attach the assembly to another microelectronic element, such as a printed circuit board. A compliant layer may be disposed between the microelectronic element and the connection component. The compliant layer typically encapsulates the leads and facilitates connection of the terminals to the contacts of another microelectronic element by compensating for variations in component flatness and the height of the terminals.
In certain preferred embodiments of commonly assigned U.S. Pat. No. 5,518,964 (“the '964 patent”), the disclosure of which is hereby incorporated by reference herein, a compliant microelectronic package is made by first connecting flexible leads between microelectronic elements, such as a chip and a connection component, and then moving the elements away from one another through a predetermined displacement so as to bend the leads. The leads may have first ends permanently attached to the connection component and second ends releasably attached to the connection component. The connection component may be juxtaposed with a semiconductor chip having contacts so that the second ends of the leads may be bonded to the contacts on the chip. Following bonding, the connection component and chip are moved away from one another, thereby vertically extending the leads. During or after movement, a curable liquid material, such as a silicone elastomer, may be introduced between the elements. The curable material may be cured, such as by using heat, to form a compliant layer surrounding the leads. The resulting semiconductor chip package has terminals on the connection component which are electrically connected to the contacts on the chip, but which can move relative to the chip so as to compensate for thermal expansion and contraction of the elements. The semiconductor chip package may be mounted to a circuit board by solder-bonding the terminals to conductive pads on the circuit board. Relative movement between the chip and the circuit board during expansion and contraction of the components is facilitated by the moveable interconnection provided by the leads and the compliant layer.
In other embodiments of the '964 patent, the package-forming process may be conducted on a wafer scale, whereby that all of the semiconductor chips in a wafer may be connected to connection components in a single step. The resulting assembly is then severed to provide individual packages, each including one or more chips and a portion of a dielectric sheet. The above-described flexible leads may be formed on a semiconductor chip or wafer, rather than on the dielectric sheet. In further embodiments of the '964 patent, a dielectric body having terminals and leads is connected to terminal structures on a temporary sheet. The temporary sheet and dielectric body are moved away from one another so as to vertically extend the leads, and a curable liquid material is introduced around the leads and cured so as to form a compliant layer between the temporary sheet and the dielectric body. The temporary sheet is then removed, leaving the terminal structures projecting from a surface of the compliant layer.
In certain preferred embodiments of commonly assigned U.S. Pat. No. 6,117,694, the disclosure of which is hereby incorporated by reference herein, a microelectronic package is made by connecting leads between a pair of microelectronic elements and then moving the elements away from one another so as to bend the leads toward a vertically extensive disposition. After bending the leads, a curable encapsulant is injected between the microelectronic elements. The encapsulant may be injected under pressure for moving the microelectronic elements away from one another and for simultaneously bending the leads. Alternatively, the leads may be vertically extended by retaining the microelectronic elements against respective platens by vacuum, and then moving the platens away from one another for bending and forming the leads. A curable liquid encapsulant is preferably injected while the platens maintain the microelectronic elements in their displaced positions.
Despite these and other advances in the art, still further improvements would be desirable.